SPC AC 231733
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1233 PM CDT THU JUL 23 2009
VALID 241200Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS UPPER MS VALLEY
REGION...LM TO IA AND NRN MO....
...SYNOPSIS...
UPPER AIR PATTERN THROUGH DAY-2 WILL CONTINUE TO BE CHARACTERIZED BY
LONGWAVE TROUGH OVER ERN CONUS AND MEAN RIDGING FROM NWRN MEX TO BC.
STG SHORTWAVE TROUGH AND ACCOMPANYING MID-UPPER LEVEL VORTICITY
LOBE IS DIGGING SEWD THROUGH SWRN PORTION OF BROADER CYCLONE OVER
NRN MB. THIS PERTURBATION IS FCST TO BECOME MAIN UPPER
CYCLONE...MOVE FARTHER SEWD...AND BY 25/12Z...COVER LS AND ADJACENT
PORTIONS WI/MN/MI/ONT. ASSOCIATED SFC COLD FRONT -- NOW ANALYZED
FROM SERN SASK INTO N-CENTRAL MT -- SHOULD MOVE EWD AND SEWD ACROSS
WRN LS...WRN WI...NRN/WRN IA...S-CENTRAL NEB...AND NERN CO BY
25/00Z. PRIMARY SFC CYCLONE SHOULD REMAIN OVER CANADA...MOVING FROM
NW OF LS TO LAKEHEAD OR NERN LS REGION BY END OF PERIOD...WHEN FRONT
SHOULD EXTEND SWWD ACROSS ERN UPPER MI...NRN IL...WRN MO...AND WRN
KS.
MEANWHILE...SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY OVER WI-- WILL PIVOT SEWD ACROSS OH BY 24/12Z THEN EJECT
NEWD OVER PA...NY...AND NEW ENGLAND DURING THIS PERIOD. IN
RESPONSE...OCCLUSION/TRIPLE POINT CYCLONE AT SFC SHOULD LIFT NEWD
OFFSHORE MID-ATLANTIC THEN ACROSS CAPE COD REGION BY 25/12Z.
TRAILING/DIFFUSE SFC COLD FRONT NOW EXTENDING FROM WRN PA TO SRN
APPALACHIANS WILL MOVE SEWD TO CENTRAL/ERN CAROLINAS AND CENTRAL GA
BY 24/12Z...STALLING DURING ENSUING 12 HOURS FROM COASTAL
MID-ATLANTIC REGION SWWD ACROSS CENTRAL/SRN GA.
FARTHER NW...SMALL MID-UPPER LEVEL LOW IS EVIDENT IN MOISTURE
CHANNEL IMAGERY OVER WRN WA AS OF 23/1630Z. THIS SMALLER SCALE
CYCLONE WILL ENTER LARGER SCALE RIDGE POSITION DAY-2...BECOMING
QUASISTATIONARY OVER ERN WA AND NRN ID. DESTABILIZATION ALOFT
ACCOMPANYING THIS FEATURE MAY CONTRIBUTE TO POTENTIAL FOR MAINLY
DIURNAL TSTMS...SOME WITH SMALL HAIL AND STG GUSTS...OVER PORTIONS
INTERIOR PAC NW AND NRN ROCKIES.
...UPPER MS VALLEY TO CENTRAL PLAINS...
SCATTERED TSTMS...SOME SVR...ARE EXPECTED TO DEVELOP INVOF FRONTAL
ZONE...AIDED BY AFTERNOON HEATING...WEAKENING
MLCINH...RICH/EVAPOTRANSPIRATIVELY-AIDED BOUNDARY LAYER
MOISTURE...AND FRONTAL LIFT. ALTHOUGH SFC FLOW AHEAD OF SFC FRONT
WILL BE GENERALLY SWLY...VEERING/STRENGTHENING OF WINDS WITH HEIGHT
IN LOW LEVELS SHOULD ENLARGE HODOGRAPHS ENOUGH TO SUPPORT POTENTIAL
FOR SUPERCELLS WITH LARGE HAIL...SVR GUSTS AND PERHAPS TORNADOES.
FCST SOUNDING SUGGEST 40-50 KT EFFECTIVE SHEAR AND 100-200 J/KG 0-1
KM SRH POSSIBLE. LONGEVITY OF SUPERCELL THREAT IS IN DOUBT ATTM
GIVEN LINEAR NATURE OF FRONTAL FORCING PROGGED IN MOST MODELS. BAND
OF STG-SVR TSTMS SHOULD MOVE SEWD WITH FRONT DURING EVENING
HOURS...GRADUALLY DIMINISHING IN INTENSITY BUT CAPABLE OF OCCASIONAL
HAIL AND DAMAGING GUSTS. MORE CONCENTRATED AREA OF GREATER
PROBABILITIES MAY EXIST IN THIS AREA AS AFTERNOON MODAL
UNCERTAINTIES BECOME BETTER RESOLVED.
CONVECTIVE AND SVR POTENTIAL BECOMES MORE CONDITIONAL WITH SWWD
EXTENT NEAR FRONTAL ZONE...DUE TO WEAKER CONVERGENCE...AND ALSO
STRONGER CINH BENEATH ELEVATED MIXED-LAYER AIR MASS.
...NERN CONUS TO ERN CAROLINAS...
SCATTERED TSTMS ARE EXPECTED TO DEVELOP DURING AFTERNOON AMIDST
DIURNALLY/DIABATICALLY WEAKENING MLCINH...ALONG/AHEAD OF FRONT OVER
ENTIRE CORRIDOR AND BEHIND FRONT...OVER PORTIONS UPPER OH
VALLEY...N-CENTRAL APPALACHIANS AND LOWER GREAT LAKES REGIONS.
WEAK LOW-MIDLEVEL WINDS WILL LIMIT BOTH CONVERGENCE AND SHEAR FROM
OH AND WRN NY EWD...HOWEVER COLD TEMPS ALOFT NEAR SHORTWAVE TROUGH
WILL CONTRIBUTE TO DESTABILIZATION IN SUPPORT OF ISOLATED HAIL/GUSTS
NEAR SVR LEVELS. GREATER LOW LEVEL MOISTURE AND STRONGER BUOYANCY
ARE EXPECTED WITH SWD EXTENT FROM MID-ATLANTIC TO CAROLINAS...AS
REGIME TRANSITIONS TO ONE MORE DOMINATED BY SEA BREEZE AND OTHER
BOUNDARY EFFECTS. MID-UPPER WINDS ALSO WILL BE STRONGER OVER THIS
REGION. A FEW ORGANIZED TSTM CLUSTERS OR BANDS CAPABLE OF STG-SVR
GUSTS ARE POSSIBLE...PRIMARILY DURING AFTERNOON. ALTHOUGH DOMINANT
MODE SHOULD BE MULTICELLULAR WITH NEARLY UNIDIRECTIONAL DEEP-LAYER
WINDS IN MOST AREAS...MID-UPPER FLOW WILL BE SUFFICIENTLY STG THAT
ANY LOCALIZED BACKING -- E.G. ALONG BOUNDARIES -- MAY SUPPORT
SHORT-LIVED SUPERCELLS AS WELL. ATTM...SVR POTENTIAL DEPENDS TOO
MUCH ON MESOBETA-TO-STORM SCALE EFFECTS FOR CATEGORICAL OUTLOOK
AREA.
..EDWARDS.. 07/23/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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